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Poliovirus Vaccine—Inactivated
HISTORICAL INTRODUCTION
Not since the introduction of the rabies vaccine by Louis Pasteur was the public interest in vaccines stirred as much as by the development and testing of inactivated poliovirus vaccine (IPV), and not since Albert Einstein had a scientist received the public adulation accorded to Jonas Salk, the vaccine’s inventor. Contributing to this phenomenon was the rise of poliomyelitis as an epidemic disease, its notoriety with the public (augmented by the paralysis suffered by US President Franklin Roosevelt), the publicity disseminated by the National Foundation for Infantile Paralysis (NFIP, a.k.a. the March of Dimes) in its effort to raise money for research, and the involvement of hundreds of thousands of US children in the trial that demonstrated the efficacy of IPV. The trial was organized by Dr. Thomas Francis and sponsored by the NFIP. It was a hallmark in vaccinology and the prototype for many later efficacy trials. The trial began in April 1954, and the successful results were announced on April 12, 1955. Licensure followed rapidly, with rapid and broad vaccine adoption in many countries.
In the early 1960s, IPV was eclipsed by oral poliovirus vaccine (OPV), except in some northern European countries. Sixty-six years after its initial development IPV is renascent, owing to improvements in manufacture, immunogenicity, supply diversity, scaling up of capacities, its outstanding safety record, major progress toward eradication of wild poliovirus circulation, and the recognition that concerns associated with OPV use (i.e., both sporadic vaccine-associated paralytic poliomyelitis (VAPP) cases and outbreaks of circulating vaccine-derived poliovirus [cVDPV]) will require total cessation of OPV use in the future. IPV, without those concerns, can provide a safety net to prevent reemergence of polio when OPV will be totally removed from routine use.
Disease caused by polioviruses is ancient. A famous Egyptian stele dating from 1403 to 1365 BC shows a man with flaccid paralysis of one leg and supported by a crutch. However, presumably owing to almost universal infection under the clinical protection afforded by maternal antibodies, only sporadic paralytic cases were described until the early 19th century when small outbreaks of acute flaccid paralysis (AFP) were noted in Europe, usually among infants living in rural areas. In 1870, Jean-Martin Charcot described the inflammatory lesions in the gray matter of the spinal cord, and in 1890, Oscar Medin described a major outbreak in Sweden, where epidemics subsequently continued to occur. Epidemics were reported in the US at the end of the 19th century, and in 1916, thousands of children were paralyzed during an epidemic in the northeastern United States. In 1908, Karl Landsteiner and Eric Popper isolated the virus of poliomyelitis, and studies of the agent began.
The key discoveries that led to IPV development were as follows:
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•Definition of the three serotypes of poliovirus by Bodian, Burnet, and colleagues.
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•Determination that poliovirus viremia precedes paralysis.
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•Confirmation that circulating neutralizing poliovirus antibodies protect against paralysis.
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•Demonstration by Enders and colleagues that the virus could be grown in cell culture.
These discoveries permitted Salk, fresh from his success in developing an inactivated influenza vaccine as well as experienced in working with poliovirus, to start IPV development. Large quantities of virus were grown in roller bottles using monkey testicular and kidney cells, and the kinetics of viral inactivation by formalin were studied. Salk concluded that if aggregates of virus were removed by filtration, poliovirus could be inactivated at a constant first-order rate, permitting complete inactivation if the process was of sufficient duration. Pools of trivalent inactivated poliovirus were prepared at Connaught Laboratories in Toronto, which were then used for vaccine formulation and filling for use in the field trial of efficacy, which was conducted by Francis and associates in 1954. Although it did have some flaws, the trial decisively demonstrated that IPV was protective, and in 1955, several US manufacturers obtained licenses for IPV and launched their products. Very soon after, similar IPVs derived from the same concepts and developed by private or state-owned institutions were launched in different countries. The Cutter incident (see “Adverse Events” below), in which recipients of IPV were paralyzed by the residual live virus in the vaccine, underlined the necessity of removing viral aggregates to permit complete inactivation but did not stop the use of IPV in many countries.
Years later, major developments improved the quality of IPV. The first, by van Wezel of the Netherlands, was the development of techniques to select the best sources of monkey kidney cells, to grow them at high density adhering to microbeads kept in suspension, and to concentrate the virus produced. The second was the adaptation of the continuous African green monkey ( Cercopithecus aethiops ) kidney cell line (denominated Vero) to the production of poliovirus by Montagnon and colleagues at the Institut Mérieux (now Sanofi Pasteur) in Lyon, France, and the development/optimization of large scale cell culture bioreactor technologies. IPV vaccine produced with the use of these improvements was termed “enhanced-potency IPV” (eIPV) to distinguish it from older vaccines made according to the original Salk method. All IPVs now in use are formulated to meet eIPV potency specifications and are referred to in this chapter as simply IPV. IPV vaccines manufactured with Sabin strain viruses were first introduced in Japan in 2012 and are now in varying stages of development in other countries (see “IPV Manufactured from Sabin Strains” later). Where relevant, these vaccines are denoted as sIPV in this chapter to distinguish them from conventional IPV (cIPV) vaccines made from wild-type poliovirus strains. The IPV acronym is used in reference to statements applicable to both types of IPV.
The description of poliomyelitis as a disease, in addition to its virology, pathogenesis, and epidemiology, is discussed in Chapter 50. However, because IPV-induced immunity depends on the immune response to the viral capsid, it is important to note that poliovirus capsids are composed of four proteins, numbered VP1 to VP4 ( Fig. 49.1 ). The first three are arranged on the surface with icosahedral symmetry whereas VP4 is an internal protein. There are five epitopes present on VP1 to VP3 that serve as virus neutralization: sites 1, 2a, 2b, 3, and 4. These vary between serotypes and between strains, and precise mapping of their tridimensional structure has identified key immune targets.
PASSIVE IMMUNIZATION
A field trial conducted in 1952 using human γ-globulin established the importance of viremia in the pathogenesis of the disease and the concept that antibodies were protective against paralysis. Protection lasted only a few weeks, rendering γ-globulin impractical as a public health strategy except in household contacts. Maternally produced antibodies transmitted via the placenta are also protective, and their half-life is only 28 days (see “Effect of Maternal Antibodies and of Neonatal Vaccination” later). Attempts are ongoing to develop humanized, camelid, or chimpanzee poliovirus-neutralizing monoclonal antibodies to treat and clear chronic poliovirus infections in immunocompromised subjects post-OPV vaccination. ,
ACTIVE IMMUNIZATION
General Principles
IPV is a mixture of the three polioviruses made by harvesting them from cell culture supernatants and submitting them to purification, concentration, and inactivation by formalin (one of the historical IPVs, developed by Lepine at the Pasteur Institute in Paris, was inactivated by formalin and β-proprionolactone). The first IPV was produced from rhesus monkey ( Macaca mulatta ) primary kidney cell cultures, with all the problems of simian viruses that might be latent or replicating actively in cultured cells. The poliovirus strains used by Salk and by the first manufacturers were wild-type polioviruses with the Mahoney (type 1, the Brunhilde strain is still used by one manufacturer in Denmark ), MEF-1 (type 2), and Saukett (type 3) strains.
Although the results of the Francis trial were positive (see “Efficacy of IPV against acute flaccid paralysis (AFP) and immune correlates of protection” later), the Cutter incident (see “Adverse Events” later) led to a change in manufacturing processes that lowered the immunogenicity of early vaccines resulting in a resurgence of paralytic polio in vaccinated children during the late 1950s, which, in turn, weakened confidence in IPV.
Fortunately, several technical advances in the 1970s led to major improvements in IPV manufacturing, which, although still based on the first-generation vaccine principles, differs in three important aspects:
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1. The cell-substrate on which the virus seeds are inoculated includes human diploid or simian continuous cell lines, rather than primary, secondary, or tertiary cell cultures from captured or bred monkeys.
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2. To increase cell density and viral yields, cells are grown adherent on microbeads kept in suspension in large bioreactors.
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3. The virus harvest is concentrated before inactivation to increase the final antigen content.
Fig. 49.2 outlines the production steps of IPV. The cells are first expanded from a working cell bank adapted to grow adherent on microbeads ( Fig. 49.3 ) in large bioreactors ( Fig. 49.4 ) until high cell density is reached. The growth medium is then removed, cells are washed, and one of the three types of poliovirus seed is inoculated. By 72 to 96 hours of incubation at 37°C, the cells are lysed by viral replication and the supernatants are collected. After clarification, the virus is concentrated by ultrafiltration. To remove residual cell proteins and DNA, the concentrated virus is passed through size exclusion and ion-exchange chromatography to yield purified material. At this point, there is less than 10 ng of DNA per human dose, a level considered to pose no hazard to recipients. The concentrated purified virus is then inactivated by incubation with formalin at 37°C for 12 days. An extra filtration is included during inactivation to remove viral clumps. Growth of polioviruses in Vero cells using animal-origin free media , and/or using genetically-engineered Vero cell lines and/or using other cell lines , , might improve compliance to pharmacopeias and/or viral yields. The final monovalent material from each serotype is tested for complete absence of residual infectivity. The three monovalent inactivated viral pools are then adjusted for antigen content, mixed, and stored as concentrated trivalent antigen bulk form until formulation of the final vaccine.
The content of the three poliovirus types in the final product, and in all intermediates, is expressed as D antigen (D-Ag) units (D-Ag are expressed only by intact virus particles). This determination was historically measured by gel diffusion in which 100 units were arbitrarily defined as the amount of D-Ag able to induce a 22-mm diameter precipitation circle in the assay that correlated with immune responses seen in the early trials performed with the enhanced potency IPV but is now assessed using enzyme-linked immunosorbent assays (ELISA). The measurement that is done on the monovalent and trivalent antigen in bulk forms constitutes the (in vitro) measurement of the potency of the product (antigenicity) and is the basis of the final vaccine formulation. All products target a specific antigen concentration for poliovirus types 1, 2, and 3 in the final product, depending on the strains used for vaccine manufacture (cIPV or sIPV), reagents, reference material used in the assay, and the data algorithm used to compute the optical density values measured in the ELISA (multiple or linear regression methods). Determination, standardization, and specifications for the D-Ag content of IPV are important issues that have complicated the emergence of the sIPV vaccines. Successive international reference reagents have been endorsed by the World Health Organization (WHO) , , and, due to the antigenic differences between cIPV and sIPV (see “IPV Manufactured From Sabin Strains“ later), suggestions have been made for the improvement of the ELISA that measures D-Ag content, or in the case of sIPV, “sD-Ag” content. , The key parameters in the performance of this assay include: (1) the nature (poly- or monoclonal antibodies used for antigen capture and their specificity[ies]) and for antigen detection, (2) the method of calculation of results (multiple or linear regression methods), and (3) the nature/origin of the reference antigen used in the assay. As a caution, some reagents may also detect the presence of poliovirus C antigens associated with noninfectious viruses consequently giving a falsely high determination of vaccine potency. ,
The immunogenicity (in vivo potency) of IPV is measured by immune responses obtained in monkeys, rats, guinea pigs, mice, or chickens. The rat model is still used in some countries for in-process controls and/or release purposes. The variability of the animal reagent, , of the methods of measuring poliovirus neutralizing antibodies, and the differential susceptibility of the Sabin and wild type viruses to trypsin and formaldehyde complicates the comparison of potencies of the different IPVs.
Finally, prediction of immunogenicity in rats from antigen content as measured by ELISA has been uncertain and the relationship between immunogenicity observed in animal models and in humans might not be straightforward.
All these parameters are surrogates for the clinical protective effect anticipated in humans vaccinated with IPV. To more closely approximate that effect, new potency assays have been evaluated like the use of transgenic mice expressing the CD-155 poliovirus receptor. , These mice can be immunized with IPV and then challenged intramuscularly with polioviruses to evaluate whether paralysis is prevented or not.
Inactivated Poliovirus Vaccine Manufactured From Sabin Strains
Because of their genomic differences, the capsid epitopes presented by the Sabin strains are different from the capsid epitopes presented by the wild-type strains and they have different sensitivities to formalin inactivation. , Using reactivity to monoclonal antibodies profiled by ELISA, it has been shown that formaldehyde inactivation does not have the same impact on the different antigenic sites presented by Sabin and wild type polioviruses. , Depending on the characteristics (reagents) of the assay to measure the antigen content and potency of resulting inactivated viruses, such alterations might not be measured. , The consequence is that sIPV and cIPV exhibit differences in their antigenicity profile, , with the result that the repertoire of poliovirus neutralizing antibodies induced in humans by cIPV or sIPV slightly differ. , In a study done at the US Food and Drug Administration (FDA) using the transgenic poliovirus receptor mouse model, a type 2 sIPV prepared by the Japan Poliomyelitis Research Institute (JPRI), elicited fivefold lower levels of MEF-1 strain neutralizing antibodies than Sabin 2 strain neutralizing antibodies and lower protection (20% to 100% paralysis, depending on dose and regimen) after virulent challenge than a type 2 cIPV prepared from MEF-1 strain (0 to 20% paralysis, depending on dose and regimen). Whether this difference has any clinical implications with regard to protection in humans against paralysis induced by cIPV versus sIPV is not yet fully clear.
The first attempts to develop sIPV occurred at the JPRI during the mid-1980s , and at the Lederle Laboratories in the US followed by the Rijksinstituut voor Volksgezondheid en Milieu (RIVM) in The Netherlands. In 2008, the WHO encouraged the entry of new sIPV manufacturers in developing countries in order to increase global IPV supply and reduce the risk of inadvertent release from cIPV manufacturing sites. , The WHO strategy included assistance to OPV manufacturers to expand and transform their manufacturing facilities, allowing them to make sIPV. To accomplish this the WHO relied on Intravacc (formerly RIVM) for technology-transfer partnerships, , which included optimization of the upstream (cell culture density, viral culture step, serum free media) and downstream (clarification, purification, inactivation) process to improve overall yields. Several companies have been awarded WHO support and have developed standalone sIPV vaccines based on this technology transfer and one company in Korea has recently achieved licensure and WHO prequalification for an sIPV developed under this program.
Other manufacturers have developed sIPVs independently. In Japan, the JPRI initiative, which started during the mid-1980s, resulted in the licensure of two combination diphtheria, tetanus, and acellular pertussis (DTaP)-sIPV products by Biken and Kaketsuken , in 2012. In China, two manufacturers have licensed standalone sIPV products since 2015, , and more are expected soon as standalone sIPV products or more complex combinations. One company has initiated the development of a sIPV based on the PER-C6 cell line platform. , ,
Inactivated Poliovirus Vaccine Manufactured From New Poliovirus Strains
Within the scope of developments that are undertaken toward lower-cost and/or safer (from a manufacturing perspective) IPV vaccines, several groups are developing new poliovirus strain seeds that could be used for vaccine production. , , Approaches are focused on developing genetically stable and hyper attenuated strains by manipulating several regions of the viral genome. Some groups are also trying to develop noncommunicable seed strains.
Adjuvanted Inactivated Poliovirus Vaccine and New Approaches
The use of adjuvants to enhance the immunogenicity of IPV antigens has been under study since the pioneering work done with mineral oil and oxide aluminum salts. , , Later, through several IPV-containing whole-cell pertussis (wP)-based combinations, the positive role of calcium aluminum salts has been advocated. Several randomized controlled trials (RCTs) have demonstrated that the immunogenicity of (DTP)-backboned combination IPV vaccines (and therefore containing aluminum salts as adjuvant) is improved compared to standalone (unadjuvanted) IPV vaccines. This is confirmed in infant primary immunization series where RCTs consistently show geometric mean titers (GMTs) against polioviruses that are approximately twofold higher with combined vaccines. Reducing the amount of antigen in standalone IPV vaccines formulated with aluminum salt adjuvants produces similar responses as recently shown by one manufacturer in Denmark with a recently licensed low-dose (4-0.8-3.2 D-Ag units/dose) aluminum-adjuvanted cIPV.
In addition, other IPV adjuvants are under investigation with a goal of antigen sparing to reduce costs and/or improving mucosal intestinal immunity. Preclinical studies with cIPV or sIPV antigens show that several new adjuvants (squalene-based or oil-in-water emulsions, toll-like receptor–agonists, polymers, chitosan, alphavirus, cytosine phosphate guanine oligodeoxynucleotides, cationic liposomes, saponin, lipopolysaccharide derivatives, and E. coli double-mutant labile toxin [dmLT]) may decrease the amount of antigen needed to achieve the desired immune responses and/or skew the response toward induction of a relevant mucosal intestinal immunity. , ,
In an effort to improve the type 2 intestinal mucosal immunity induced by cIPV, and in the context of the tOPV to bOPV 1&3 switch that occurred in 2016 (see “Chapter 50, Poliovirus Vaccine-Live“) clinical trials of a high-dose (32 D-Ag units) monovalent type 2 cIPV showed higher type 2 humoral responses compared with cIPV, but intestinal mucosal immune responses and viral shedding post-mOPV2 challenge were similar (see “Mucosal Immunity/Protection Induced by IPV” later). , , ,
Finally, technical innovations supported by WHO, PATH, and the Bill and Melinda Gates Foundation (BMGF) that are under investigation include: micro-array/needle, dissolvable or not, patches for transdermal delivery of antigens, , injectable microparticle formulations allowing pulsed/controlled-release of antigens, , plant-based antigen synthesis platforms, , recombinant virus-like particles, drying of antigens for better thermostability of final vaccines, and intranasal or sublingual administration routes. , However, most of these approaches have yet to achieve proof-of-concept or the promise of industrial feasibility and scalability and affordability compared to currently marketed IPV formulations.
Vaccine Constituents Other Than Immunizing Antigens
Antibiotics may be used in the manufacturing of the viral (cell) working seeds (banks), and/or in the viral culture to prevent bacterial contamination, but are largely eliminated during purification. Many manufacturers are engaged in removing antibiotics during the working viral seeds or cell banks, and/or viral culture manufacturing steps; nevertheless, the use of polymyxin B does have some effect on the quality of viral replication. When included in multivalent combination vaccines, the quality of the IPV bulk antigens and of their other constituents are of extreme importance in the behavior, potency, and stability of the formulated final drug product.
Thimerosal cannot be used as a preservative in multidose IPV formulations/presentations because it reduces antigenicity. , When required, preservation of the final product in multidose containers can be conferred by residual formalin and 2-phenoxyethanol. The recently updated WHO multidose vial policy states that preserved multidose (2-, 5-, or 10-dose) vial presentations of IPV can be used up to 28 days after first use provided they are handled according to good vaccination practices and stored between usages at 2°C to 8°C.
Stability
IPV is stable for 3 years at 2°C to 8°C. Its thermal stability varies, as expected, with the level and duration of out-of-normal storage temperature excursions. When exposed to freezing temperatures, IPV loses antigenicity in the D-Ag assay while not necessarily immunogenicity in the rat potency assay. , The same observation can be made when IPV is exposed to high temperatures. Most multidose products used in tender-driven public markets are equipped with vaccine vial monitors to measure cumulated temperature exposure.
Producers of Inactivated Poliovirus Vaccine Antigen and Available Vaccines
Table 49.1 lists the current manufacturers of IPV antigen (drug substance) used in vaccines that are distributed as of end of 2022 or that are under development. In recent years massive global scale-up of production has occurred with the licensure and deployment of several new suppliers, and it is expected that the global annual capacity for production of IPV vaccines will further increase, enabling broader use of IPV.
TABLE 49.1
Manufacturers of Inactivated Poliovirus Vaccine Bulk Antigen Used in Licensed/Distributed or Under Development Vaccines (as of end of 2022)
| Manufacturer | Where Made | Cell Substrate |
|---|---|---|
| Wild-type strains based IPV | ||
| Bilthoven biologicals BV (Serum Institute of India) | The Netherlands | Vero |
| GlaxoSmithKline | Belgium | Vero |
| Sanofi Pasteur | France | Vero |
| AJ-Vaccines A/S (formerly Statens Serum Institute) | Denmark | Vero |
| Sabin strains based IPV | ||
| Institute of Medical Biology (Chinese Academy of Medical Sciences) | China | Vero |
| Japan Poliomyelitis Research Institute (Biken Group and KM Biologics Co., Ltd) | Japan | Vero |
| BIBP-CNBG (Sinopharm) | China | Vero |
| WIBP-CNBG | China | Vero |
| Sinovac | China | Vero |
| Minhai | China | Vero |
| Janssen Vaccines & Prevention (Johnson & Johnson) | The Netherlands | PerC6 |
| LG Chemical | Republic of Korea | Vero |
All available IPVs contain inactivated viruses for the three serotypes, and are available either as standalone vaccines (most unadjuvanted) or as trivalent (Td-IPV), tetravalent (DTaP-IPV and Tdap-IPV), pentavalent (DTaP-IPV-Hib and DTaP-IPV-HB), and hexavalent (DTa/wP-IPV-HB-Hib) aluminium-adjuvanted combination vaccines (see also Chapter 16). Those vaccines are used worldwide for infant/toddler primary immunization series and/or for booster immunization at school entry age, and for adolescents and adults. Some of these vaccines are also used for immunization in persons (most often adolescents or adults) not previously immunized or with unknown or incomplete immunization history. In several markets, standalone or less often IPV-combination vaccines are formulated, filled, labeled, packaged, and released by a national manufacturer using IPV bulk antigens imported from another manufacturer. Up to 18 to 36 months are needed from engaging working viral seed lots in the production of the vaccine antigens to batch release of the packaged final IPV-containing vaccine by all (internal and external) control laboratories for a given market, particularly with complex DTP-combination vaccines. The complexity of the industrial manufacturing flows of the IPV vaccines (and of their intermediates) and the lability of the product mix demands from the different customers explains the dynamic of the market supply.
Most IPV standalone vaccines are WHO prequalified and are compliant with the WHO technical recommendations. , , Some are manufactured in compliance with the third edition of the WHO Global Action Plan To Minimize Poliovirus Facility-Associated Risk After Type-Specific Eradication Of Wild Polioviruses and Sequential Cessation Of Routine OPV Use (GAPIII). The adoption by all manufacturers of these requirements has been the subject of intense discussion, and the requirements imposed on the handling of Sabin type 2 strain from April 2016 (similar to those applicable for wild-type strains, which are mainly directed to handling viruses in BSL3+ environments) has added complexity for Sabin IPV manufacturers.
The first DTP-IPV vaccines were licensed in 1964 in France and the United Kingdom and contained cIPV and diphtheria and tetanus toxoids combined with whole-cell pertussis (DTwP), but today DTwP-cIPV–containing combinations no longer exist. Several manufacturers have embarked on the (re)development of wP-IPV-based hexavalent combination vaccines including cIPV or sIPV antigens. , One challenge associated with DTwP-IPV combination vaccines is to manage the bidirectional deleterious effect on polio and pertussis potency caused by residual thimerosal (associated with the non-IPV antigens) and residual formaldehyde and 2-phenoxy-ethanol (associated with the IPV antigens), respectively, in the final vaccine formulation.
Dose Responses, Dosing, and Route of Administration
Jonas Salk established that the immune response to cIPV is directly related to the dose of antigen. The antigen content of contemporary cIPV vaccines is derived from a series of dose–response clinical trials , , performed in infants from 1977 to 1979, designed to establish the optimal D-Ag content for reliable protection against paralysis after two doses of cIPV combined with other vaccine antigens (D, T, and wP routinely administered at the same age). This strategy was implemented by Jonas Salk and Charles Mérieux with the objective of developing and qualifying a cIPV formulation that would be useful in Africa and would require only two doses separated by a long interval to overcome the negative effect of circulating maternally transmitted poliovirus antibodies on their first dose immune responses. These studies led to the current cIPV formulations with 40, 8, and 32 D-Ag units for poliovirus types 1, 2, and 3, respectively (this content corresponding to a vaccine formulation target determined by multiple-regression analysis of D-Ag content of monovalent and trivalent antigen bulks measured by ELISA). These trials showed that the 40:8:32 D-Ag unit formulation was immunogenic in schedules consisting of two consecutive priming doses followed by a booster administered at least 6 months following the last infant priming dose to generate long term immunity. It should be noted that some of these studies documented the capacity of cIPV to induce antibody levels after the first dose, which was confirmed in a one-dose clinical efficacy of 36% (95% confidence limits, 0% to 67%) measured in Senegal during a WPV1 polio outbreak (see “Efficacy of IPV Against AFP and Immune Correlates of Protection” later). , ,
Numerous infant/toddler primary immunization series regimens are in use globally. All IPV-only using countries rely on IPV-containing combination vaccines, and the so-called “3+1” and “2+1” schedules are the most frequently used regimen with three (or two) doses during the first 6 months of life followed by a booster during the second year of life. Some countries administer the booster at school-entry age (“2+0+1”). The subject of additional boosters at the school-entry age or beyond is discussed later (see “Duration of Immunity”). Some countries supplement IPV vaccination in infancy with OPV booster doses given later in childhood or with OPV delivered by supplemental immunization activities designed to control poliovirus transmission (see “Results of Vaccination Programs with IPV” later).
The ideal dosage for cIPV in unvaccinated adolescents and adults is three doses. The first two doses can be given 1 or, preferably, 2 months apart, with the third dose given 6 to 12 months later (acting as a booster). Adolescents or adults who have been primed during infancy and whose last polio vaccination occurred 10 to 20 years ago need only one booster dose to redevelop high titers. , In adult subjects with an unknown polio vaccination history, two doses of cIPV-containing combination vaccines given 1 month apart are sufficient to induce very high seroprotection rates and persisting circulating antibodies. ,
IPV may be given subcutaneously or intramuscularly, and there is no published information from RCTs on the relative immunogenicity (or safety) of IPV administered intramuscularly versus subcutaneously; however, as IPV is administered increasingly frequently as an IPV-containing DTP-backboned combination vaccines (that are designed to be administered intramuscularly), and as the objective is to minimize local adverse events, IPV is generally administered intramuscularly, even when used as a standalone vaccine.
RESULTS OF VACCINATION
Measurement of Immune Responses
Although it is possible to measure serum antibodies to poliovirus by classical immunoenzymatic methods, the poliovirus-neutralizing antibody assay best correlates with protection against paralysis. Cell-mediated immune responses have been explored in response to cIPV , , but are not routinely used except for research purposes. They have shown the presence of specific T cells (by lymphoproliferation tests and flow cytometry) in the blood following vaccination. Measurement of mucosal immunity biomarkers induced by IPV is discussed later (see “Mucosal Immunity/Protection Induced by IPV”). Pseudovirus neutralization, fluorescence adherence inhibition, binding inhibition ELISA, or multiplexed PCR-based neutralizations assays are under development, some of them being compatible with restricted use of infectious poliovirus strains.
IPV is a killed multi-epitopic antigen to which immune responses depend on the antigen content, the number of doses (when used for primary immunization), the interval between doses, the age at a first dose (and, consequently, the level of maternally acquired poliovirus antibodies that are present at time of vaccination, which can reduce immune responses), and the type of IPV-containing product used (e.g., unadjuvanted vs aluminum-adjuvanted IPV-containing vaccines). Several metrics are used to describe the level of neutralizing antibodies against polioviruses in a group of vaccinated individuals including GMTs or median titers (which can lead to different results compared with GMTs); the percentage of subjects with neutralizing antibodies at or above the 1 : 8 threshold now considered as the serological correlate of protection against paralysis (historically a 1 : 4 threshold was used) and generally used to determine the seroprotection rate; and the percentages of subjects who develop a fourfold or greater rise in their neutralizing antibody titers between the prevaccination and postvaccination timepoints, adjusted or not for maternally derived antibody decay, and referred to as seroconversion. If maternal antibody decay is not taken into account, seroconversion rates could be lower than the actual proportion of persons who experience a significant rise in their antibody level. It is known that maternal antibody inhibits the immune response to the first dose of IPV, including both cIPV and sIPV (see “Effect of Maternal Antibodies and of Neonatal Vaccination” later).
The poliovirus neutralization antibody assay is used by all laboratories to assess the humoral immune response to IPV. The assay procedures are variable and have been shown to be sensitive to the cell line used to grow the target virus (HEp-2 or Vero), the viral inoculum size, the duration and temperature of serum–virus incubation before viral growth, the number of serial dilutions of the tested sera, and the target viral strains (Sabin or wild type) used in the test. , In addition, the type of assay readout (cytopathic effect or metabolic inhibition) has an influence. Attempts have been made to standardize this assay, , but there is no broad acceptance of international standards for its use. Under many assay conditions, neutralizing titers are higher when sera from subjects vaccinated with cIPV are tested against wild-type strains compared to when tested against Sabin strains. , As described in “IPV Manufactured from Sabin Strains” earlier, it is likely that the paratopes (antigen-binding sites) of the neutralizing antibodies generated in sIPV-vaccinated subjects differ from the paratopes in cIPV-vaccinated subjects, and that the overall levels of neutralizing antibodies measured in these subjects are influenced by the viral strains used in the detection system. In the landmark historical studies, which led to studies underlying the develoment of the current cIPVs, , , the serum neutralization assays were based on wild-type–derived poliovirus strains. Due to a historical indifference to poliovirus strain choice and the risks of handling wild-type–derived strains, many laboratories, particularly for those located in polio-free areas or in low- or middle-income countries, have converted to the use of the Sabin strains for the neutralization assay. In the future, it is likely that safer novel OPV vaccine strains will be adopted for use in the neutralization assay by many laboratories in order to meet changing global health biocontainment requirements. This parameter should be considered when comparing antibody levels from clinical trials, particularly those done with sIPVs. The three-dimensional mapping of the poliovirus epitopes and antibody interactions will provide more detailed information on this question.
Immunogenicity of Conventional Inactivated Poliovirus Vaccine
Numerous studies and trials have been conducted over the last 40 years using different formulations of cIPV, study designs, and schedules, and conducted in a variety of countries spanning the socioeconomic spectrum. Table 49.2 summarizes data collected from 30 study groups where cIPV-containing vaccines were administered to more than 4500 subjects in a two-dose primary series, usually at 2 and 4 months of age. At the completion of the two-dose immunization series, seroprotection rates ranged from 89% to 100% for poliovirus type 1, from 92% to 100% for poliovirus type 2, and from 70% to 100% for poliovirus type 3. Table 49.2 also summarizes responses after three doses. Seroprotection rates after three doses are clearly higher than after two, particularly when the schedule is 2–4–6 months. However, schedules of 3–4–5 and 2–3–4 months also give good responses, although lower than the 2–4–6 month schedule, particularly the GMTs. To achieve rapid protection in developing countries, infant vaccines are given on a 6–10–14-week schedule according to Expanded Programme on Immunization (EPI) convention, which is not optimal for the immune response against several antigens because of the early age for starting immunization and the short interval between doses. Since the initial studies sponsored by the WHO, many studies have been done in a wide range of epidemiological settings with different cIPV-containing vaccines. Many of these studies were conducted in countries where tOPV was routinely used and cIPV vaccinees could have been exposed to Sabin polioviruses via contact with tOPV or tOPV-vaccinees ( Table 49.3 ) (Sanofi Pasteur, studies HIT40498, EUV07199/HE9810, and A3R25 and A3R38; unpublished, data on file). , In general, high seroprotection rates were achieved at completion of the immunization series, however, when reported, seroconversion rates, were more variable, presumably because of the high maternal antibody levels observed in some studies. In one study in South Africa (Sanofi Pasteur, study A3R25 and A3R38; unpublished, data on file), antibodies were measured at 17 months of age after three doses of cIPV contained in a hexavalent combination vaccine given in infancy, and persistence of antibodies with a good anamnestic response to a fourth dose were noted. At 17 months of age, 100%, 99.5%, and 97.8% of children had neutralizing antibodies at titers greater than or equal to 1:8 against poliovirus types 1, 2, and 3, respectively, and a 40- to 56-fold increase in GMT was observed from prebooster to postbooster. Similar observations were noted in another trial in the Philippines. A direct comparison of the 2–4–6-month and the EPI schedule was performed in Puerto Rico, where tOPV was no longer used. Seroconversion rates for types 1, 2, and 3, respectively, after three doses of the 2–4–6-month schedule were 100%, 100%, and 99%, whereas after the EPI schedule they were 85.8%, 86.2%, and 96.9%, respectively. Overall, the data demonstrate that cIPV is immunogenic in an EPI schedule, although the titers achieved and the seroconversion rates may be lower compared with vaccination of infants at older ages. The humoral immunogenicity of cIPV in an EPI schedule has long been considered to be superior to OPV in developing countries with poor sanitation, although this has not been a consistent observation, particularly in recent studies. , , , After two or three doses in the first 6 months of life, antibody levels fall although the vaccinees usually retain seroprotective titers until the first booster is given during the second year of life, and this third (or fourth) dose stimulates a marked anamnestic response. Table 49.4 presents five studies conducted in the US. Nearly all infants were seropositive after the second dose, although their antibody titers were generally below 1:100. Race and ethnicity background have never been observed to be clinically relevant factors in the immunogenicity profile of IPV.
TABLE 49.2
Summary of Immunogenicity of cIPV After Two or Three Doses in the First Year of Life 1 Month After Last Vaccination
| Schedule | Type 1 | Type 2 | Type 3 | Study Groups | Approximate No. Subjects | |||
|---|---|---|---|---|---|---|---|---|
| Seroprevalence | GMT | Seroprevalence | GMT | Seroprevalence | GMT | |||
| 2–4 mo | 89%–100% | 17–355 | 92%–100% | 17–709 | 70%–100% | 50–1200 | 30 | 4500 |
| 2–4 and 12–18 mo | 94%–100% | 495–2629 | 98%–100% | 1518–6637 | 97%–100% | 1256–4332 | 10 | 2000 |
| 2–4–6 mo | 96%–100% | 143–2459 | 96%–100% | 78–2597 | 95%–100% | 187–3010 | 48 | 6000 |
| 3–4–5 mo | 85%–100% | 110–475 | 98%–100% | 92–944 | 86%–100% | 89–1244 | 8 | 500 |
| 2–3–4 mo | 93%–100% | 143–595 | 89%–100% | 91–561 | 95%–100% | 221–1493 | 18 | 2200 |
cIPV, conventional inactivated poliovirus vaccine; GMT, geometric mean antibody titer.
Data from Vidor E, Meschievitz C, Plotkin SA. Fifteen years of experience with Vero-produced enhanced potency inactivated poliovirus vaccine. Pediatr Infect Dis J . 1997;16:312–322.
TABLE 49.3
GMT and Percentages of Subjects Who Seroconverted (or With Poliovirus NA ≥1:8) After IPV-Containing Vaccines at 6, 10, and 14 Weeks of Age
| Study | References | Postdose 3 Poliovirus Antibodies | ||
|---|---|---|---|---|
| Type 1 | Type 2 | Type 3 | ||
| Oman, 1990–1992 | ||||
| Product used | DTwP-IPV | |||
| GMT | 447 | 571 | 251 | |
| % seroconverted | 88% | 92% | 91% | |
| Gambia, 1990–1991 | ||||
| Product used | DTwP-IPV | |||
| GMT | 79 | 144 | 241 | |
| % seroconverted | 81% | 82% | 98% | |
| Thailand, 1991–1992 | ||||
| Product used | DTwP-IPV | |||
| GMT | 49 | 68 | 136 | |
| % seroconverted | 66% | 63% | 92% | |
| South Africa, 1998 a | ||||
| Product used | DTwP-IPV/Hib | |||
| GMT | 116 | 93 | 166 | |
| % with NA ≥1:8 | 99.2% | 99.2% | 99.2% | |
| Philippines, 2000 b | ||||
| Product used | DTaP-IPV-Hib | |||
| GMT | 863 | 768 | 901 | |
| % with NA ≥1:8 | 100% | 100% | 100% | |
| Moldavia, 1998 | ||||
| Product used | DTaP-IPV-HepB | |||
| GMT | 535 | 154 | 731 | |
| % with NA ≥1:8 | 98.7% | 98% | 98.7% | |
| Moldavia, 1998 | ||||
| Product used | DTwP-IPV/Hib | |||
| GMT | 170 | 88 | 544 | |
| % with NA ≥1:8 | 99.3% | 97.2% | 100% | |
| Cuba, 2001 | ||||
| Product used | DTwP-IPV/Hib | |||
| GMT | 304 | 304 | 858 | |
| % seroconverted | 94% | 83% | 100% | |
| South Africa, 2001 c | ||||
| Product used | DTaP-IPV-HepB-Hib | |||
| GMT | 1226 | 661 | 1249 | |
| % with NA ≥1:4 | 100% | 100% | 100% | |
| Philippines, 2003 | ||||
| Product used | DTaP-IPV/Hib | |||
| GMT | 533 | 789 | 1968 | |
| % with NA ≥1:8 | 100% | 100% | 100% | |
| Puerto Rico, 2003 | ||||
| Product used | IPV | |||
| GMT | 222 | 147 | 724 | |
| % seroconverted | 85.8% | 86.2% | 96.9% | |
| South Africa, 2005 | ||||
| Product used | DTaP-IPV/Hib | |||
| GMT | 1453 | 1699 | 2395 | |
| % with NA ≥1:8 | 100% | 100% | 100% | |
| India, 2006 | ||||
| Product used | DTaP-IPV/Hib | |||
| GMT | 440 | 458 | 1510 | |
| % with NA ≥1:8 | 100% | 99.1% | 100% | |
| South Africa, 2006 | ||||
| Product used | DTaP-IPV-HepB-Hib | |||
| GMT | 579 | 620 | 975 | |
| % with NA ≥1:8 | 100% | 98.5% | 100% | |
| Philippines, 2008 | ||||
| Product used | IPV | |||
| GMT | 585 | 795 | 774 | |
| % seroconverted | 98.2% | 98.2% | 100% | |
a Sanofi Pasteur. Study HIT40498; unpublished, data on file.
b Sanofi Pasteur. Study EUV07199/HE9810; unpublished, data on file.
c Sanofi Pasteur. Study A3R25 and A3R38; unpublished, data on file. DTaP, diphtheria, tetanus, and acellular pertussis vaccine; GMT, geometric mean antibody titer; HepB, hepatitis B vaccine; Hib, Haemophilus influenzae type b vaccine; IPV, inactivated poliovirus vaccine; NA, neutralizing antibodies.
TABLE 49.4
Studies of IPV Given Alone or in IPV Followed by OPV Sequential Schedules: % of Neutralizing Antibody to Indicated Strain ≥1:8 (Geometric Mean Titer)
| Reference | Vaccine Administered at Given Age (Month) | After Second Dose | After Third Dose a | Before Booster | After Booster b | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No. c | 2 | 4 | 6 | 12–18 | Type 1 | Type 2 | Type 3 | Type 1 | Type 2 | Type 3 | Type 1 | Type 2 | Type 3 | Type 1 | Type 2 | Type 3 | |
| Faden et al. , | 116 | IPV | IPV | IPV | 96 (184) | 100 (631) | 96 (634) | 90 (61) | 96 (135) | 92 (102) | 96 (1954) | 100 (5835) | 100 (5187) | ||||
| 34 | IPV | IPV | OPV | 100 (283) | 100 (481) | 100 (1132) | 100 (128) | 100 (334) | 100 (151) | 100 (3044) | 100 (10,693) | 100 (2347) | |||||
| Blatter and Starr | 94 | IPV | IPV | IPV | 97 (44) | 96 (105) | 95 (83) | 92 (22) | 95 (42) | 87 (23) | 100 (2070) | 100 (3419) | 100 (1968) | ||||
| 68 | IPV | IPV | IPV | 98 (88) | 100 (256) | 98 (162) | 100 (41) | 100 (71) | 93 (35) | 100 (2029) | 100 (4388) | 100 (2580) | |||||
| Halsey et al. | 75 | IPV | IPV | OPV | 94 (28) | 98 (91) | 96 (63) | 85 (18) | 96 (47) | 81 (20) | 100 (1568) | 100 (7199) | 96 (297) | ||||
| 99 | IPV | IPV | OPV | 99 (90) | 99 (120) | 95 (126) | 98 (47) | 96 (61) | 88 (29) | 100 (1765) | 100 (7516) | 99 (709) | |||||
| Onorato et al. | 87 | IPV | IPV | IPV | OPV | 97 (74) | 98 (82) | 100 (110) | 100 (463) | 100 (652) | 100 (605) | 100 (72) | 100 (98) | 100 (91) | 100 (2141) | 100 (7169) | 100 (1824) |
| 331 | IPV | IPV | IPV | 99 | 99 | 99 | 99 | 100 | 100 | ||||||||
| Modlin et al. | 332 | IPV | IPV | IPV | 99 | 100 | 100 | 100 | 100 | 100 | |||||||
| 101 | IPV | IPV | IPV | 97 | 92 | 78 | 100 | 100 | 100 | ||||||||
| Asturias E et al. | 113 | IPV | IPV | IPV | 100 (1011) | 99 (517) | 99 (859) | 100 (2542) | 100 (2675) | 100 (3248) | |||||||
| 920 | IPV | IPV | OPV | 99 (1284) | 100 (798) | 99 (1089) | 100 (1821) | 100 (4294) | 100 (2828) | ||||||||
| 101 | OPV | OPV | OPV | 97 (575) | 100 (1641) | 94 (350) | 99 (685) | 100 (1768) | 98 (415) | ||||||||
b Booster is third or fourth dose, depending on the schedule.
c Number of enrolled subjects at beginning of study. IPV, inactivated poliovirus vaccine; OPV, live oral poliovirus vaccine.
Immune responses are detected after the first dose of cIPV-containing vaccines and depending on study design, seroconversion rates up to 50% against the three poliovirus types are observed (on average 33%, 41%, and 47% of vaccinees seroconvert against types 1, 2, and 3, respectively, with better one-dose seroconversion at older ages up to 6-9 months). Persons who fail to seroconvert may yet be primed, and, when using as a definition of priming the detection of neutralizing antibody 7 days after second vaccination in persons still seronegative prior to that dose, one trial revealed that up to 90% of seronegative vaccinees were primed. As summarized later under “Efficacy of IPV Against AFP and Immune Correlates of Protection,” a one-dose schedule provided limited clinical efficacy (36% with 95% confidence limits ranging from 0% to 67%) against wild poliovirus type 1 in a case-control study in Senegal, estimates that track observed seroconversion rates for one and two doses, respectively. , , Similarly, a study in Tamil Nadu, India found that 3 IPV doses delivered 92% efficacy.
In contrast, Hungary eliminated VAPP with a single IPV dose, an observation compatible with priming offering clinical protection against paralysis from IPV priming. These data are important in the context of efforts by WHO to develop affordable IPV vaccines for the developing world (see “Rationale and Role of IPV in Poliomyelitis Eradication” later).
To summarize, the main determinants of IPV immunogenicity are the number of primary series doses (with increasing seroconversion rates by cumulated doses), the age at first dose (with improved responsiveness with aging), the interval between doses (with boost-like responses with 4-month and longer intervals), the presence of maternally transmitted antibodies (with decreased responses), and the use of IPV in the form of an IPV-containing combination vaccine (with higher responses due to the adjuvant effect).
Immunogenicity of Sabin Inactivated Poliovirus Vaccine
Because comparison of the relative D-Ag content between sIPV and cIPV is not possible due to differences in in vitro (D-Ag determination by ELISA) and in vivo (immunogenicity in animals) potency assays used to formulate and release these vaccines , , , , , , the results of the clinical evaluations of sIPVs can only be summarized product by product.
Murph and colleagues at Lederle in the US performed a study in 1986 in which 18 seropositive adults received sIPV vaccines containing 10-6.25-17.5 D-Ag units, 20-12.5-35D-Ag units, or 40-25-70 D-Ag units (types 1, 2, and 3, respectively) per dose and nine seronegative adults who received one dose of the 20-12.5-35 D-Ag unit formulation. In the seropositive adults, the three vaccine formulations boosted serum neutralizing antibody levels with a noticeable dose–response effect. In the seronegative adults, a response against the three polioviruses was observed. All subjects in this trial had previously received OPV or cIPV during infancy and there were no subjects who received a control injection. Infant studies with this vaccine were not reported.
Two clinical trials were conducted by the JPRI in the early 1990s with a standalone sIPV vaccine. Phase I was conducted in adults and in 108 infants 3 to 90 months of age. The D-Ag content of the vaccine was 30-30-50 D-Ag units/dose. In the first trial, the vaccine was given in two subcutaneous doses to 10 seropositive adults at 4-week intervals. Safety was excellent. Antibody titers obtained 2 weeks after the second dose (against Sabin and wild-type strains) showed high neutralizing responses in all volunteers. In the second trial, the vaccine was given by the same regimen to 108 infants (3–90 months old). Most infants were seronegative (titer <1:4) before immunization, except for type 2 where 40% were seropositive. Immunogenicity results 2 weeks after the second dose showed a high neutralizing response in all infants against types 1 and 3, but a lower neutralizing response for type 2. Serum neutralization GMTs against the homotypic Sabin strains were approximately 2000 for polio type 1, 300 for polio type 2, and 500 for polio type 3 but GMTs were fourfold to 1.3-fold lower against wild-type strains compared to the homotypic Sabin strains. In 2002, JPRI reformulated the sIPV content on the basis of new immunogenicity data obtained from rats and monkeys to contain 1.5-50-50 D-Ag units/dose (types 1, 2, and 3, respectively). Two similar DTaP-sIPV tetravalent combination vaccines were licensed in Japan in 2012 that contains the JPRI sIPV (Biken and KM Biologics Co., Ltd). Each of these products induced a 100% seroprotection against the Sabin strains following a three-dose primary series in infants 3 to 8 months of age with a 1-month interval between doses and durable antibody levels. When assessed against wild-type strains, 97.4% to 100% of sera exhibited levels equal to or above the 1:8 threshold, but their GMTs were lower (10- to 20-fold less for type 1, twofold less for type 2, and 1.5-fold less for type 3) than when tested against Sabin strains. , Similar data were published from a third manufacturer. ,
The Institute of Medical Biology at the Chinese Academy of Medical Sciences (Kunming Institute) has performed a multistep Phase I study in adults, children, and infants with several sIPV formulations containing from 15-16-22.5 to 45-64-67.5 D-Ag units for poliovirus types 1, 2, and 3, respectively, with good immunogenicity and a dose–response effect. Following this study, a Phase II dose–response (three formulations) and comparative trial against OPV and cIPV was conducted in infants. A content of 30-32-45 D-Ag units was then selected for a Phase III comparative trial versus cIPV. This vaccine was licensed in China in 2015 and then followed by Phase IV data. Cross-neutralization evaluation of Phase II vaccinees’ sera against a panel of wild type strains (Mahoney, MEF-1, and Saukett), the three Sabin strains, one recent wild-type type 1 Chinese isolate, and several non-Chinese vaccine-derived polioviruses [VDPVs] strains showed that the mean levels of antibodies able to neutralize the non-Sabin strains in sIPV vaccinees were lower compared to levels induced in cIPV vaccinees. Nevertheless, more than 95% of vaccinees developed seroprotective antibody titers in neutralization assays against Sabin viruses and wild type viruses. Additional trials with this vaccine, in the form of a DTaP-sIPV tetravalent combination, as a component of various sequential regimens with bOPV vaccine are ongoing. Additional Chinese manufacturers (BBIBP-CNBG, Wuhan Institute of Biological Products (a subsidiary of CNBG), Beijing Minhai Biotechnology Co. Ltd.) are deploying similar approaches with vaccines containing varying D-Ag units per dose and are engaged in multiple clinical trials.
Finally, Intravacc (former RIVM), a partner in the WHO technology transfer program cited above, has explored the dose–response effect of several unadjuvanted and aluminum-adjuvanted sIPV vaccine preparations. Phase I clinical trials have been conducted in adults in Poland and Cuba , with a standalone sIPV product (20-32-64 D-Ag units/dose) versus an aluminum-adjuvanted standalone sIPV product (10-16-32 D-Ag units/dose) versus a cIPV and a Phase IIa dose-escalating trial has been completed in infants in Poland, with three formulations of an aluminum-adjuvanted sIPV or three formulations of an unadjuvanted sIPV standalone product (six arms) versus a control standalone cIPV. The results showed adequate safety of the products and the capacity of both formulations to induce neutralizing antibody against Sabin strains (and against wild-type strains with as expected lower levels) with a dose–response effect and a moderate adjuvant effect. The first sIPV (5-8-16 D-Ag units/dose) developed under this program by a commercial manufacturer was recently licensed by LG Chemicals, Ltd., in South Korea and prequalified by WHO.
In addition, a PER.C6 cell line-derived sIPV has been tested in cIPV-primed adults and shown to stimulate strong booster responses.
Because sIPV presents to the immune system different epitopes associated with neutralization than cIPV, sIPV vaccinees also have different humoral immune response profiles. The recent adoption of an international standard for sIPV D-Ag content expressed in Sabin D Antigen unit (sDU) will facilitate comparison among all sIPV vaccines, including those originally developed with the use of the D-Ag as a measure of vaccine potency. ,
The breadth and duration of polio vaccine-induced intratypic immunity have been questioned due to an outbreak of disease by a type 1 poliovirus that was only weakly neutralized with OPV immune sera. , Thus, it will be important to continue to document the immunogenicity of the licensed sIPVs and to assure that antibody response in humans is broadly cross-reactive against all types of strains. To date, there are little data that address the interchangeability of cIPV and sIPV or their sequential administration.
In addition, the level of intestinal and oropharyngeal mucosal immunity against infection and viral shedding, relative to cIPV’s performance, achievable with the licensed sIPV is not yet documented.
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